Cycles rendering looks strange and simplified
This looks like an accidental Layer Material override. Check if your active render layer has a material set in the data field indicated in red in this screenshot:



Such an override replaces every single material on the RenderLayer with the one selected. It's useful for adding custom AO passes, Clay Renders, or diagnostic renders.

Click the small X icon next to the material to remove the override, and you should be back to normal.

By the way: By default the viewport renderer does not take Render Layer modifications into account. That's why you get a different result between the two. You need to explicitly tell Blender to do this using this Toggle Button while a viewport render is running: